On October 6th, 2012 at approximately 7PM a female victim while waiting to board an Orange Line train at Tufts Medical Center station noticed a male enter into the paid area without paying, he "piggybacked" in. The male proceeded over to the victim with his pants unzippered and was manipulating himself. The female victim screamed and attempted to walk away from the male, however he followed close behind her the entire time masturbating. The victim contacted Transit Police and reported the incident. An investigation was commenced. On October 14th, 2012 at approximately 8:20 PM the victim was once again at Tufts Medical Center station and observed the male who had committed the above acts standing on the platform. The courageous and quick thinking victim immediately contacted Transit Police and officers assigned to Area 1 responded and stopped the male to further investigate. The victim positively identified the male as the man who was exposing himself to her and masturbating. Officers placed the male, later identified as Juan Pena, 23 of Boston,MA., under arrest for Open and Gross conduct and transported him to Transit Police HQ. Pena will appear in Boston Municipal Court sometime today.